Explanation:
At a level closer to the surface of the planet, the centripetal force increases. In a circular orbit, the centripetal force is provided by the gravitational force, which is proportional to the inverse square of the distance from the center of the planet.

The kinetic energy in a closer orbit is larger since the centripetal force is larger. Making the speed larger is necessary to maintain the orbit, which therefore increases the kinetic energy.

Explanation:

The hydrogen nucleus is a proton, so it has positive charge.

The electric field lines are pointed upwards, meaning the higher potential is below the nucleus, or meaning that the force on the nucleus is upward.

The question asks for the largest work done, therefore we are looking for the largest displacement parallel and in the opposite direction the field lines. This is shown in D.

Explanation:
The pattern of equipotential surfaces belongs to two like charges. That indicates that field direction at points A and B should be in the same direction. Additionally, field lines and equipotential surfaces are at right angles to each other. The only answer that satisfies these conditions is A. Therefore, the answer is A.

Explanation:
Recall that magnetic force acts perpendicular to current flow according to the Fleming Left hand rule. That immediately eliminates option A and D. Then using the right hand grip rule, we can determine that the magnetic field experienced by wire $Y$ points into the page. The force direction and magnetic field direction allows current direction to be found with Fleming’s left-hand rule.

The electric field at X due to -Q points toward -Q. The field at X due to +Q points away from +Q, with the same magnitude at X as the field from -Q. Adding the electric field vectors gives a vector pointing to the left.

1/4

Explanation:

When the bar magnet moves towards and away from the ring, the magnetic flux through the ring will change. According to Lenz's law, an emf, and therefore a current is induced to oppose the change in the flux. So as the bar magnet approaches the metal ring, the metal ring moves to the right due to repulsive forces that resist the decrease in distance between the ring and the magnet. Likewise, as the bar magnet moves away from the metal ring, the metal ring moves to the left.

Explanation:
Choice A is incorrect as it equates the gravitational field strength with the gravitational force and these two are two different physical quantities.

Choice B is the correct answer, since the gravitational field strength equals to force per unit mass; g=F/m.

Choice C is incorrect, because the gravitational field strength is inversely proportional to the square of the distance between the center of mass of the planet and that point; g=GM/r^2.

Choice D is incorrect, because the gravitational field strength depends on the mass of the planet; g=GM/r^2.

4g

Explanation:
The direction of the current is perpendicular to the magnetic field in both regions and the magnitude of the field is unchanged. So the magnitude of the force is $F$.

Using Fleming's left hand rule, direction of the force is

Explanation:
The $20nC$ charge produces a leftward electric field in region 1. Therefore, the electric field generated by the $X$ charge should be rightward to cancel the electric field of the 20 nC charge. This is achieved by a negative charge at X. The magnitude of the electric field decreases by distance. All locations in region 1 are closer to point charge $X$ than they are to the $20nC$ charge. Therefore X should be smaller than the charge of $20nC$. The answer is D.

Explanation:
Equipotential lines are perpendicular to field lines, which means the field lines must be directed from A to B or vice versa. That is only possible for 2 charges with opposite sign. In I and II, the forces from the two objects would be in opposite directions, giving a resultant field zero at the midpoint, and equipotential lines of a “peanut” shape.

Explanation:
The force acting on the electron is downward at entry and perpendicular to the velocity, and the electron has negative charge. Using conventional methods (right-hand/left-hand) the magnetic field vector points into the plane of the paper

Explanation:
Because the electric field is only in the vertical direction, it does not affect the electrons' horizontal speed.

As described by E=F/q in the data booklet, the electrons do experience a vertical force which causes them to accelerate vertically.

Therefore when they enter the electric field, the horizontal speed of the electrons remains the same while their vertical speed increases

Explanation:
The alpha particle has positive charge, therefore its deflection will be in the opposite direction of the electron. (answer A or B)

It has a larger mass, therefore the acceleration will be much smaller, explained by the following calculation:

• qE=ma
• a=qE/m

The alpha particle has twice the charge of the electron, this doubles its acceleration.

It has much more mass than the electron, therefore the denominator in the above ratio increases by a larger factor than the numerator. This means the acceleration of the alpha particle will be much smaller than that of the electron. (its motion will change at a slower rate).

This can also be explained by 2-dimensional motion where there is no force on the horizontal but there is a smaller force on the vertical, meaning it will cover the vertical distance in a longer time, allowing it to travel further along the horizontal, giving the path in B.

Explanation:
Centripetal acceleration of an orbiting satellite is the gravitational acceleration of the planet, which is given by

g=GM/r^2

Since the gravitational acceleration is inversely proportional to the square of the orbital radius, the correct graphical representation is given in C

Explanation:
Conventional current will flow anticlockwise due to the orientation of the cell. To determine the force experienced by a current carrying conductor in a magnetic field, use (any appropriate hand-rule convention or) Flemming's left hand rule which states that if we arrange our thumb, forefinger and middle finger of the left-hand perpendicular to each other, then the thumb points towards the direction of the force experienced by the conductor, the forefinger points towards the direction of the magnetic field and the middle finger points towards the direction of the electric current.

Explanation:
According to Newton's third law, the two objects exert equal and opposite forces on each other.

The equation

• Fg=GMm/r

also shows that the forces on the planets are equal in magnitude.